16in Rokit

I decided to build this monster after the NC was donated to me.
It wasn't really a rocket nosecone but it will work for the project.

Target weight is 50lb so I can fly it on 3in M motors.

This is a link to a PDF drawing of its design(14.3kB)

Screen shot

Summary

This is a basic 3FNC design.

The fins have to be removable so I have designed that in.
I also want it to be a coupler-less design.
What that means is that there will be two sections of the rocket but they wont use a coupler to join them.
They will simply disconnect from each other at apogee.

Nose Cone

The nose cone that started it all

Body Tube

The tubes arrive!

I started this project with a 16in Sonotube.
That is too heavy so I decided to use it as a mandrel for a glass tube.

I made up two foam rings to center the tube on a 1in pipe

I had to sand the tube so it was smooth then I put mylar film over the tube.
I then put 1 layer of 6oz carbon, 2 layers of uni-directional 6oz glass and 2 layers of 6oz boat glass.

Tube glassed

Tube pulled

This light construction for the outer 16in tube makes a fairly flimsy tube so I decided to do a biaxial tube design.
With this I used an 8in sonotube I had as a mandrel and made some strong 8in tubes out of 2 layers of carbon and 4 layers of 6oz glass.

One 8in tube is mounted inside each of the 16in sections with 3 centering rings each.

8in and 16in tubes

I was going to do some sort of pyro release to seperate the two halfs but time ran short so I simply made an 8in coupler out of the sonotube I had.
I made one cut length wise down the tube then glued it back together.
The 1/8in kurf of my table saw blade reduced the OD by about .04in.
Enough to get a couple wraps of CF and glass on there.

Coupler waiting for glass

Fins

I need the fins removable so I can fit it in my car for transport.
I also wanted them light to keep overall weight down and to cut down on nose weight.

I initially wanted to use 1/4in plywood but I needed sheets at least 24x24 and didn't have time to order online.
I opted to use 1/2in foam from Home Depot
I put 2 layers of 5.7oz CF and 2 layers of 6oz unidirectional glass on each side.
This made for a very light and strong fin.
The original 1/2in ply fins I cut were 40oz each w/o any composit on them.
The completed foam fins were only 30oz each!! That saved me 7.5lb in the tail.

I decided to use a sub fin.
This is cut the same size as the fin but with a span of only 4in. It is also only 1/4in plywood.
This reinforces the fins at the root but reduces the overall weight.
I didn't like the weight of the 1/4in ply so I cut lightening holes in it.

Filling lightening holes

It looked like a muffin assembly line.
I realized I didn't have enough foam to finish so to keep things balanced I only foamed half the holes in each fin.
I filled the remaining holes with balsa wood rings.

Filling with balsa

There are two sub fins for each fin.
I put glass on the inside and CF on the outside of each sub fin.

Sub fins tack down

I tacked down the sub fins with the fin in place then removed the fin so I could glass them
In the picture above you can see the 1/2in gap where the fin slides down between them and gets bolted in place.

Sub fins glassed

I put generous fillets around the outside (CF side) then one layer of 6oz fiberglass tip to tip. I then put a strip of 6in wide glass across the fillet area.

Rail guides

I like to put nice strong blocks for my rail guides to mount to.
I used 3/4in plywoood cut roughly 2in square.
I shape one side to conform to the curve of the body tube.
A 1/4in tee nut is inserted into the back of the block.
These were bolted in place with two stainless #8 bolts as seen in the following photo.
You can almost make out the vaseline that I filled the threads and hole with.
This keeps the epoxy out of the hole/threads when I mount the body tube.

Rail guide mounts

I take my angle and lay it across the CR's then mark the location of each mount and also the position of the aft CR.
This helps me locate them once the airframe is installed.

Rail guide mount locations

Test Fit

Time for a test fit and photo op...

Looks good

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